1. Field of the Invention
The present invention relates to a magnesia-spinel refractory having improved corrosion resistance and slag penetration resistance and used for a high-temperature metallurgical furnace, a cement rotary kiln, and the like for steel refining, nonferrous metallurgy, etc.
2. Description of the Related Art
A conventional magnesia ultra-high-temperature refractory is disclosed, which comprises a fused magnesia clinker as an aggregate, and a spinel solid solution phase containing an alumina component in an amount of 5 to 40% by weight relative to the entire matrix (refer to, for example, Japanese Patent Unexamined Patent Publication No. 4-55360). Japanese Unexamined Patent Publication No. 5-117019 discloses that magnesia-chrome or magnesia-spinel basic refractory bricks (a type of ceramics) are mainly used for a high-temperature metallurgical furnace, a cement rotary kiln, or the like for steel refining, nonferrous metallurgy, etc, and the magnesia-spinel refractory bricks are generally produced by mixing two raw materials, i.e., 50 to 90% by weight of magnesia (MgO) clinker and 10 to 50% by weight of spinel (MgO.Al.sub.2 O.sub.3) clinker.
However, in molding and burning a mixture of magnesia clinker powder and spinel clinker powder, the spinel phase is not sufficiently produced in the crystal grain boundaries of periclase crystals, which are magnesia crystals, and thus a magnesia-spinel refractory having a high density and a strong structure cannot be obtained. Furthermore, since a mixture containing magnesia clinker and spinel clinker a- powders each containing coarse particles (particle diameter of about 1 to 3 mm), medium particles (particle diameter of about 250 .mu.m to 1 mm) and fine particles (particle diameter of 250 .mu.m or less) is molded and burned, the apparent porosity of the resultant refractory is about 10% or more, thereby failing to obtain a dense structure. Therefore, the refractory has problems in that it is easily corroded with melted slag and melted cement, or easily worn by structural spalling and abrasion.